A. ROLE OF CORE This core serves as the center for data processing and cohort maintenance for the Nurses' Health Study. Thus it supports this program project and the other funded research grants that draw on the questionnaire based exposure data from the cohort. Within this program project, the core serves projects 1,2, 3, and 4 by providing exposure data for all analyses and it links to Core B where diseases reported on the follow-up questionnaires are subsequently documented.